When a conventionally frozen fruit is thawed a dark, soft, mushy product is often obtained. Moreover above disadvantages are often accompanied by "bleeding" of liquid from the thawed tissue, a phenomenon which is also known as drip loss.
Heat treatment of frozen food prior to freezing has been suggested in the past; however, none of the known methods was able to significantly overcome the negative effects of freezing on fruits and vegetables and most of the suggested methods actually imparted cooked characteristics to the food products.
Dehydrofreezing of peeled fruits has been suggested, such as in Canada Patent no. 1,275.196, wherein prior to freezing the fruit pieces were blanched in water at a temperature ranging from 85.degree. C. to 95.degree. C. and subsequently dried by means of hot air at a maximum temperature of 60.degree. C., until the weight of fruit pieces were reduced to substantially half the weight.
Israel Patent nos. 41493 and 41494 disclose dehydrofreezing processes for peeled bananas and cut avocado respectively, which are dehydrated prior to freezing in a forced draft drier in a tunnel oven. However, a treatment of bananas and avocado in air convection ovens forms a "skin" on the outer surface of the freshly diced fruit--the phenomenon is also related to as formation of case hardening. Case hardening is easily detected by the consumer who declines using such treated product.
Microwave treatment of frozen food prior to freezing has been disclosed in the past, such as in Chemical Abstract 44643r or chemical Abstract 157043h. However, above publications disclose microwave blanching, that is a brief scalding in order to lower microbial count and reduce enzyme activity, or in order to impart cooked characteristics on the final product. Similarly EP Patent no. 72878 discloses a process for preparing frozen diced food suitable for pets in which the foodstuff is first treated with microwaves which raise the temperature at the center of the foodstuff to at least 75.degree. C.
It is the object of the present invention to provide frozen fruit and vegetable in which the thawed tissue will retain a fairly normal texture and flavor and thus the organoleptic characteristics be maintained.